This invention relates to a method for the preparation of a spin-coating precursor solution for perovskite material, specifically of La1xe2x88x92x(Caxxe2x88x92yPby)xMnO3 (LCPMO, in which x=0xe2x88x920.5 and y=0xe2x88x92x), and a method for LCPMO thin film deposition via spin-coating technology. Additionally, a method to reversibly change LCPMO thin film resistance is incorporated into the method of the invention.
Materials having a perovskite structure, such as colossal magnetoresistance (CMR) materials and high temperature superconductivity (HTSC) materials, have a number of uses in the IC field. An important characteristic of CMR and HTSC materials is that their electrical resistance may be changed by external influence, such as a magnetic field or an electric field, and by temperature changes, making their use in many IC applications desirable. They can sense magnetic fields,which provides improvements in the data density and reading speed of magnetic recording systems; and they can sense heat and some light wavelengths, which provides a material for thermal and infrared detectors, as well as material for photo and X-ray detection. Because a static electric field can trigger the collapse of an insulating charge-ordered state of CMR materials to a metallic ferromagnetic state, they may be used in micrometer- or nanometer-scale electromagnets.
HTSC materials are primarily used as superconductors, and their conductivity may be modified by an electric current or a magnetic field. They may also be used as a conductive layer in the epitaxial multilayer structures for use at room temperature. As previously noted, temperature, magnetic fields, and static electric fields can change the electrical characteristics of CMR and HTSC materials, however, these stimuli do not permanently alter the states or permanently modify the properties of these materials. Thus, when a stimulus vanishes, the changed material""s state or property will return to its original value. The resistance of CMR materials will change when a large magnetic field is applied As the magnetic field strength increases, the resistance of the CMR material decreases. As the strength of the magnetic field decreases, and returns to zero, the resistance of the CMR material will return to its original value. However, very low temperatures cause a relatively large resistive lag in CMR materials, as is the case in ferromagnets, which exhibit a magnetic lag. According to the prior art, because CMR materials only respond to large changes in magnetic fields, or changes in static electric fields only at very low temperatures, CMR materials have not been considered practical for use in IC applications.
Reversible resistance change is a basic requirement for potential resistance based non-volatile memory devices. The prior art in this area is related to the disclosure of perovskite thin films, and specifically Pr0.3Ca0.7MnO3 (PCMO) metal oxide thin films, which demonstrated a reversible resistance change ability through the application of electric pulses. PCMO thin films are grown on epitaxial YBa2Cu3O7 (YBCO) and partial epitaxial platinum substrates, via pulsed laser ablation (PLA) technique. PCMO thin films having reversible resistance change characteristics are the subject of Liu et al., Electric-pulse-induced reversible resistance change effect in magnetoresistive films, Applied Physics Letters, 76, 2749, 2000; and Liu et al., U.S. Pat. No. 6,204,139, granted Mar. 20, 2001, for Method of switching the properties of perovskite materials used in thin film resistors. Pr0.3Ca0.7MnO3 (PCMO) thin films are shown to have reversible resistance change properties via applying electric pulses at room temperature. Liu et al. demonstrated that resistance change may be controlled by adjusting the polarity of electric pulses: resistance increases under the influence of a positive pulse, and resistance decreases under the influence of a negative pulse. XRD polar figures in the Liu et al. references indicated epitaxial properties of PCMO thin films. The integration structures of PCMO thin films disclosed by Liu et al. included PCMO/YBCO/LAO, PCMO/Pt/LAO and PCMO/Pt plate. The reference and patent indicate the probability that CMR materials have reversible resistance change properties at room temperature. A method of manufacture of the resistance based, or PCMO or CRM materials, for use in non-volatile memory devices is not taught by the references.
A method of forming a perovskite thin film includes preparing a perovskite precursor solution; preparing a silicon substrate for deposition of a perovskite thin film, including forming a bottom electrode on the substrate; securing the substrate in a spin-coating apparatus and spinning the substrate at a predetermined spin rate; injecting a perovskite precursor solution into the spin-coating apparatus thereby coating the substrate with the perovskite precursor solution to form a coated substrate; baking the coated substrate at temperatures which increase incrementally from about 90xc2x0 C. to 300xc2x0 C.; and annealing the coated substrate at a temperature of between about 500xc2x0 C. to 800xc2x0 C. for between about five minutes to fifteen minutes.
It is an object of the invention to establish a method for the manufacture of a resistance-based non-volatile memory device.
Another object of the invention is to provide a method of compounding precursors for the fabrication of perovskite thin films, and specifically LCPMO thin films.
A further object of the invention is to provide a method of compounding a perovskite precursor suitable for spin-coating deposition.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.